1. Field of the Invention
The invention relates to electrical circuit assemblies and, more particularly, to electrical circuit assemblies which supply a resistor for measuring electrical parameters.
2. Description of Related Art
Battery powered electronic devices often include electronics for monitoring the current of the battery cell. Excessive current in either of the charging or discharging directions can damage the cells or compromise the safety of the device. One technique for monitoring cell current entails connecting a sense resistor between the positive and negative terminals of the battery cells in series with a load or charging element. A discrete sense resistor having a low resistance, for example less than 1 ohm, causes only a small voltage drop in the total cell voltage so that cell current is measured without affecting the device operations. Unfortunately, a sense resistor having suitable accuracy is bulky and expensive. Furthermore, such a sense resistor has a high temperature coefficient so that typical variations in operating temperature result in unacceptable fluctuations in cell current measurements.
To avoid the disadvantages of measurement circuits incorporating a sense resistor, some designers have utilized a conducting MOSFET in series between the battery cells to serve as a resistor as well as a disconnect switch. However, disadvantages arise in a MOSFET implementation due to the great lot-to-lot, temperature and gate drive variability of MOSFET devices.